Molded cathodes



June 1l, 1957 J. cRoNlN 2,795,033

Filed Jan. 31, 1952 5 E *il Arum/:y

June l1, 1957 .1.. J. cRoNlN 2,795,033

MOLDED cATHoDEs Filed Jan. s1. 1952 s sheets-sheet 2 3 Sheets-'Sheet 3 FVG.

W//AlWf L.. J; CRONIN MOLDED CATHODES r Il!!! June 11, -1957' Filed Jan. 51, 1952 /A/i/,s-f/ra/P fa J. awa/W www y This 'invention relates to a method for maufacturing molded .cathodes and more particularly relates to a method for Jommg molded ceramic cathodes to metal supports.

atet Theppresent method of joining molded ceramic cath` odes, such as cathodes containing a substantial proportion of thoria, to, metal supports involvesthe use of platinum solder.y These soldered cathode assemblies are undesirable since platinumvaporizes at the cathode operating temperature of high powered tubes such as magnetrons and migrates over the cathode surfaces, thereby inhibiting the emission of electrons; moreover, platinum solder is veryv expensive. Other less expensive soldering alloys are unsatisfactory either because of ltheir extremely low melting pointsV orbecause of their inability to Wet the ceramic cathode surface. k. Sintering of the metal supports directly to the ceramic cathodes is inelfective since a refractory metallic powder, such as molybdenum powder, alone will not adhere firmly to the ceramic cathode.y

In accordance with the present invention, the inside of the mold' in whichY 4the cathode is tol beformcd is coated with a thin layer of-a powdered refractory` metal suspended in a suitable binder. This coating is yso applied to the moldV that after-the compacting. operation it will be lofive percent powdered thoria' and twenty-five percent pow- Y dered molybdenumg Bushings v'10 and 11 arernext placedk cated in the form of a thin film or layer adjacent each end .l

of.4 the cathode at the `proper distances from the active A portion in the center. The ceramiccompact is then `removed frorn the mold and tired in a furnace containing a non-oxidizing atmosphere at a temperature in the range of approximately'LSOO degrees C. to 2,300 degrees C. for about one-half hour. vAt the conclusion of the firing, the refractory metalllmbecomes bonded tenaciously to the thoria compact. After machining these cathodes to size,

they may be joined to metallic cathode supports which may or may not be of the same refractory metal as the metallic film or layer on the cathode. By molding the molybdenum powder into the body of the cathode in the manner just described, the cathodes may be firmly and economically joined to the metallicvsupports either by a conventional soldering or sintering process.

An object o f this invention is to produce a firmly adherent'layer of metal which is molded on the surface of molded ceramic cathodes.

A further object of this invention is to produce a ceramic to metal bond which can be easily produced and which will withstand considerable stress.

Still another object of this invention is to produce a ceramic cathode which may be readily and rmly joined to metal cathode supports by a conventional soldering or sintering operation.

Other and further advantages of this invention will be describedl later. i n f ICC Fig. 3 is a fragmentary longitudinal section view of a portion of the mold of Fig. 1 illustrating the manner of applying a coating to the sleeve of said mold;

Fig. 4 is a fragmentary view of a portion of a coated sleeve segment of the mold shown in Figs. '1-3;

Fig. 5 is a view similar to Fig. 3 illustrating the manner in which the mold core is coated;

Fig. 6 is a section view illustrating one type of molded cathode;

Fig. 7 is a section view illustrating a second type of molded cathode;

Fig. 8 is a transverse section view of one modification of a cathode assembly;

Fig. 9 is a fragmentary longitudinal section View of a second modification of a cathode assembly;

' Fig. l0 is a partial vertical section showing the details of Fig. 9; and

Fig. 11 is a development of one of the sheet metal supa fixed support 2 and Vincludes a cylindrical body `Sprol vided'with a tapered bore 4 throughwhich a plurality of sections 5 of a sectionalsleeve 14 having an outer surface which follows the contour of bore 4 may be inserted.

The segments 5 .of the-sleeve 14," here shown as three in number, are assembled and fitted into bore 4 under pressure and the sectional sleeve defines a cylindrical .bore r.

A tubular bushing 9 is mounted on 'the lower endV of the core 8 and said bushingand core are'inser'ted intobore 6. The annular space between the outer surface of core 8 and7 bore 6 is filled with a desired quantity of powdered ceramic material 'l capable of substantial thermionic emissio'm' which may comprise; for example, a mixture of seventyover core 8 and aeram 12 positioned above core 8 as shown in Fig. 1. A pressure of about 200,000pounds per square inch isapplied to the upper surface of ram 12 so that the mixture 7 betweenbushings 9 and 10 is compacted. After removing the sleeve 14 from the mold body 3,"the sleevey is disassembled and the moldedcylinder 7 formed'fromthe compacted powdered mixture is removed. The molded cylinder must then be Vheat treatedin a -manner tobe 1n Fig; 3 a seetionaliview `ef they mold of Fig. t1 is shown with ycertain parts removed in the interest of clarity. The inner surface 6 of sleeve 5 iscoated with f thin layers' 15 and 15 of a powdered refractory metal suspended in ak suitable binder. For example, a paste made up of molybdenum powder held together by a solution of nitrocellulose in 'amyl acetate is applied vto the surface 6 of sleeve segments 5, as shown in Figs. 3 and 4. The three sleeve segments are assembled, the bushing 9 placed over cores and the bushing and core inserted into 4bore 6. The powdered mixture containing thoria is poured into the mold to a level equal to the compression ratio times the desired length of the compacted cathode body. The areas over which theV sleevel segments are 'r coated depend in part upon the compression ratio of the coating 15 is applied adjacent the top surface of thevv powdered mixture in the mold. See Figs. 3 and 4. After the pressure operation is completed, layers or lms 25 and 25' of molybdenum will be molded intomolded cathode 7, as shown in Fig. 6. The compacted cathode Patented June 11, 1957 3 7, after.removalsfromnthez-moldgr is next Ytired4 to give it mechanical.. strength.. and...electnicalH conductance... The.` compacted `cathode 7 is placed -in a furnace containing an atmosphere of hydrogen or aneatmosphere which is nonoxidizingtin charactenandfheated wateapproximately 1,800 5 degreesf:C;. about .f-.onef'halfrhou Ai temperaturen ranger. of from about 1 1,800i degrees-aC; to :2,300gdegreesxQ lm aY-j l bet. used` fonsatisfactoryiresultsf ,Theirbinden is driyen off during l1eating,;and.:the-.molybdenumilayersfZS:and;` 25;v `become-firmly :moldedsintortheibodyof the; thoria 10 cathode 7 at the ends thereof-.iatstheaconclusionl of:the l firingi.. Theselayers 25r1and25i; beingmf :metallic mate.- rial, make possible the satisfactory jointure of said'acathode .toa .metallic supportiatlthe-region'occupieth by said layer. l Y V One ,z form fof.:` directly: vheated f cathode1 assembly including the molded cathode of Fig. 6 is shown in Fig.- 8 Zand. comprises; a. cathode: assembly, generally. indicated.; by numeral 20, whichzincludesian:electromemissive cathode in -theform of the molded cylindrical-sleeve!! land adapted 20 to be supported between an outer tubular electrically con ductingrmember` 18, madenof a refractory electrically conductive material, such-` asA molybdenum, anda cap or l support 19,rp1:eferably` made of the.` samel materialN as support member` 18. An inner conducting rody 21, 25 mounted coaxial with outer conductor 18 Vand cathode 7, is .threaded at one end 22 to `receive conductingcap 19. The supports 18 .and i19are shouldered to support cath-s ode 7. Whena suitable voltageis applied between conductors 18 Vand 21, the current passing throughcathode y30 7 heats the latter to the-temperature of thermionic emis-v sion.

The portions'ZS and 25,' of the cathode 7 'may be-connected securely to cathode supports 19 and 18, respectively;4 either by sintering with a refractory metal powder, 35 suchfas'molybdenum powder, ort-bysoldering with a solderxhavinga highs meltingpoint?, suchasr'iridium and A` second example, ofia directly? heatedf-cathodeas-A sembly, particularly suitable. forrelectronf dischargegdev-ices 40 ofthemagnetron type, isshown Vin fFigr 9;: yAntelectron emissive cathode'Tfis preferably constructedin the form of a .cylindricalsleeve by compressinga mixture of pow-V dered thoria (thorium .oxide)`and' a powdered "refractory l metaljsuch as :,molybdenum, inV a mold such as: shown iniL Figs. 1 and 2 and in: armanner tobe described subsequent-vly. Acylindrical sheet'metal supporting sleevetlsf; which f may be: constructed of t molybdenum, is securedftothe` lowerfend-offcathodef While'` aA similar supporting sleeve. 19' is likewise secured to the upper end ofcathode 7': 50 Supporting. sleeves 18 land19'extend into-opposite ends ofi cathodef :7' a short t distance sufricent 4to i provide for rigidjoints ybetweenlthesupports land fthe cathodes. yThe supporting sleeves mayfbe stampedr outy of a thin -sheet metal blanleandlbentzintocylindrical-,Shaper Asshown in-Fig.` l1, the supporting. sleeves Emay ybetprovided-with a pluralityof longitudinali paralleli rectangular slots 27 equallyspaced Varound .the peripheryof fthe cylinder: Midway "betwcenzadjacent pairs offrectangularsIotsi-27 pluralitysr of;spaced f tabs 28 is.` formed 'by :making three-sided 60 cuts in 'support blank 119' and fbending the .'.sh'eet material' outwardly f atxrightzanglesv'to therzplanegof the blank; as i shown imFigsi. 10 `land", l 1. Metallic sleevel 18'sv is formed in: the .samemannerV as: upperl sleevey19T. l As shown in- Figrf '10; tliexlower surface of: tabsZS-of-upper sleeve-19- 65 will: engage..l the t upper: end surface of cathode- 7'. Similai'ly;H the ai upper.` surfaces rof 'tabs 29 "'of-flov'ver sleeve 18 will:.engagethelower-end :surfacel ofthe cathode. y Tabs*` 28rand-:29aid-ifin positioning sle'evesJ 19'fand18'f relative tothefcathode prior to jointureand aid in;` preventing motion of the=cath'ode'relative-to the sleeveszduringrtlre joining operation.- TherectangularA slotsfZ'T: make ,the endscf the-supportingsleeves flexiblefto allow forA the differential expansion `of 'thecathode and 'its support and f greatly reduce the relative moyementbetween cathode. and..

support and, consequently, the strain on the joint therebetween. It should. beunrlerstood,A however, that vthe, rectangular slots and tabs may be eliminated and the cathode supports 18 and 19 made from a solid blank of sheet metal.

A metallic bushing 23 having a. shoulder portion and preferably made of the same sheet metal stock as the supporting sleeves, is soldered to the upper end of sleeve 19', as shown in Fig.-9. A shallow disk 24 is` placed inside bushing 23 with itsf lower face resting `on and ;se-.,. cured to the upper face of the4 bushingV shoulden A metallic conducting rod 21' is soldered or othcrwsefastened to the bottom of disk 24.` When a proper voltage is appliedbetween l-support18' and conducting rod 21', a current passes through cylindrical cathode 7', thereby heating the latter to the temperature of thermionic emission. If the thoria cathode sleeve is to be connected to a cathode support of the type shown in Figs.l 9 and .10, it is obvious that, `since the metallic supports are adapted to surround thev cathode, adjacent the ends thereof, `the molybdenum films or layers 26. and 26 which are to Vbe bonded to the thoria cathode should be located Von the. inner surface of the cathode. This type of molded lcathode, as -shown in Fig. 7, is formed in the same manner as the-cathode of'Fig. 6` exceptv that the paste comprising,- the binder and molybdenum powder is applied tothecorc 8 ofthe mold,` as shown at 16 and 16"in Fig. `5, rather than to the surfaces of the segments of the mold sleeve.V The actual connection of the `thoria cathode .to the-sup-4 ports of Fig. 9 `is accomplished inthe same manner as in` the case of the cathode assembly of Fig, 8.

It is also feasible to moldthe cathode" by exertioncf lateral pressure, as, for example, by the hydro-static method. A rubber core may be used instead of a hard, core 8 so that the core is distended sidewise orrat right` angles to the axis of the core. In this manner, the metalized paste may be applied over a more limited por.-v tion of the mold and the transfer of the metalized layer,` to the thoria 4compactwill be more readily and definitely accomplished;

While two cathode assemblies` are described aridillus:` trated herein, it should ybe understood thaLothe'r type cathode assemblies may. beincluded 'withinthe scope .of this invention. It is obviously possibleto manufacture, molded cathodesofvarious sizesY and .shapesdepending upon theY configuration. off the` mold.` Other..` methods l,of-r molding` may also beused. Furthermore, the.; location.V and .number of [molded `layers ofrefractory metal may, be varied, dependinguponthe arrangementof and .the.nurn ber of connections to be made between cathode and cath-g odesupports.

Whatis claimed is: l

l. A? method of f manufacturing. molded V.ceramic cathy odes .capable of being. securely joinedto ,metahsupportm comprising coating alportionof theinnerperiphcgypof a mold sleeve with a thinlayer of powdered refractory,-` metal suspended in aV binder, inserting-Ain said-,mold-4 a desired `quantity of a powdered mixture containing-a largeA percentage of a ceramic capable ofJ therrnionic; emission;y removing said ,refractory metalfrorn said portionllofgsaid mold sleeve andcompacting rsaid-powderedminture and. said refractory metal yby exerting pressure onf, saidzmold.' to` thereby forma moldedcathode into theoutcnsurface of, which `a 4layer: of said lrefractoryymetal `is tmoldcdn..

2. A method of manufacturing ,molded thoria, cathodes:` capable of being securely joined to metalgsupportsl come. prising` coating portions off- -a mold," which: are: spaced .a predetermined-distance apart with athi'n layerlopowf. der edlrefraetory metal suspended: insa binder, inserting in .i said mold a desired quantity of a powdered mixture `cone. taining ya large percentagefof a.ceramic.capablev of therm-` ionic emission, renloving said refractory:metalyfromfsaidz portions of said mold and compactingsaid."mixtureand;` said refractory metal by;exertinggpressuremnfsaidgmpld thereby forming a moldedcathodefintoportions:of `wluiset surface a layer of said refractory metal is molded, and firing said cathode until said metal layer is firmly bonded to said cathode.

3. A method of manufacturing molded ceramic cathodes capable of being securely joined to metal supports comprising coating portions of a mold which are spaced a predetermined distance apart with a thin layer of powdered refractory metal suspended in a binder, inserting in saidl mold a desired quantity of a powdered mixture containing a large percentage of a ceramic capable of thermionic emission, removing said refractory metal from said portions of said mold and compacting said mixture and said refractory metalby exertingpressure on said mold thereby forming a molded cathode into portions f Whose surface layers of said refractory metal are molded, removing said cathode from said mold, and firing said cathode at a temperature of at least 1,800 degrees C. until said metal layers are firmly bonded to said cathode.

4. A method of manufacturing molded ceramic cathodes capable of being securely joined to metal vsupports comprising coating portions of a mold which are spaced a predetermined distance apart with a thin layer of powdered refractory metall suspended in a binder, inserting in said mold a desired quantity of a powdered mixture containing a large percentage of a ceramic capable of thermionic emission so that the top and bottom surfaces of said mixture coincide with said coated portions of said mold, removing said refractory metal from said portions of said mold and compacting said mixture Aand said refractory metal by exerting pressure on said mold therebyL forming a molded cathodev into which spaced layers of said refractory metal are molded, removing said cathode from said mold, and firing said cathode at a temperaturev of from approximately 1,800 degrees C. to approximately 2,300 degrees C. until said metal layers are firmly bonded to said cathode. f

5. A method of manufacturing molded ceramic cathodes capable of being securely joined to metal supports comprising coating a portion of the inner surface of a mold sleeve with a thin layer of powdered refractory metal suspended in a binder, inserting a core in the circular bore defined by said sleeve, inserting a desired quantity of a powdered mixture containing a substantial proportion of a ceramic capable of thermionic emission in the annular space between said sleeve and said core, compacting said mixture and said refractory metal so as to form a molded cathodeinto a portion of whose outer surface said refractory metal layer is molded, removing said cathode from said mold, and firing said cathode in an oxygen-free atmosphere at a temperature of approximately 1,800 degrees C. to approximately 2,300 degrees C. until said metal layer is firmly bonded to said cathode.

6. A method of manufacturing molded ceramic cathodes capable of being securely joined to metal supports comprising coating a portion of the surface of a mold core with a thin layer of powdered refractory metal suspended in a binder, inserting said core in the circular bore of said mold defined by a mold sleeve, inserting a desired quantity of a powdered mixture containing a large percentage of a ceramic capable of thermionic emission in the annular space between said sleeve and said core, compacting said mixture and said refractory metal so as to form a molded cathode into a portion of whose inner surface said refractory metal layer is molded, removing said cathode from said mold, and firing said cathode in an oxygen-free atmosphere at a temperature of approximately 1,800 degrees C. to approximately 2,300 degrees C. until said metal layer is firmly bonded to said cathode.

7. A method of joining molded ceramic cathodes to metal supports comprising coating spaced portions of a mold with a thin layer of powdered refractory metal suspended in a binder, inserting a desired quantity of a powdered mixture containing a large percentage of a ceramic capable of thermionic emission in said mold, removing said refractory metal from said portions of said mold and compacting said refractory metal by exerting pressure on said mold to thereby form a molded cathode into which spaced layers of said refractory metal are molded, removing said cathode from said mold, firing said cathode in an oxygen-free atmosphere at a temperature of from approximately 1,800 degrees C. to approximately 2,300 degrees C. until said metal layers are firmly bonded to said cathode, and joining metallic cathode supports to said bonded metal layers on said cathode.

8. A method of joining molded ceramic cathodes to metal supports comprising coating portions of a mold with a thin layer of powdered refractory metal suspended in a binder, inserting a core in said mold, inserting a desired quantity of a powdered mixture containing a substantial proportion ofy a ceramic capable of thermionic emission in the space within the mold unoccupied by said core, compacting said mixture and said refractory metal so as to form a molded cathode into portions of whose surface said refractory metal layers are molded, removing said cathode from said mold, firing said cathode in an oxygen-free atmosphere at a temperature of from approximately 1,800 degrees C. to approximately 2,300 degrees C. until said metal layers are irmly bonded to said cathode, and joining metallic cathode supports to said bonded metal layers on said cathode.

9. A method of joining molded thoria cathodes to metal supports comprising coating portions of a mold which are spaced a predetermined distance apart-with a thin 4layer of powdered refractory metal suspended in a binder, inserting in said molda desired quantity of a powdered mixture-containing a large percentage of a ceramic capable'of thermionic emission so that the top and bottom surfaces of said mixture coincidewith said coated portions of said mold, removing said refractory .y

metal from said portion 4of said mold and compacting said mixture and said refractory metal by exerting pressure on said mold thereby forming a molded cathodeinto which spaced layers of said refractory metal are molded, removing said cathode from said mold, firing said cathode at a temperature of from approximately 1,800 degrees C. to approximately 2,300 degrees C. until said metal layers are firmly bonded to said cathode, and joining a metallic cathode support to each of said bonded metal layers on said cathode.

l0. A method of joining molded ceramic cathodesto metal supports comprising coating a portion of a mold with a thin layer of powdered refractory metal suspended in a binder, inserting a core in said mold, inserting a desired quantity of a powdered mixture containing a substantial proportion of a ceramic capable of thermionic emission in the space within the mold unoccupied by said core, compacting said mixture and said refractory metal layer so as to form a molded cathode into which said refractory metal layer is molded, removing said cathode from said mold, firing said cathode in an oxygenfree atmosphere at a temperature of from approximately 1,800 degrees C. to approximately 2,300 degrees C. until said metal layer is firmly bonded to said cathode, and sintering a metallic cathode support to sai-d bonded metal layerlon said cathode by means of a powdered refractory meta 11. A method of joining molded thoria cathodes securely to metal supports comprising coating a portion of a mold with a thin layer of powdered refractory metal suspended in a binder, inserting a core in said mold, inserting a desired quantity of a powdered mixture containing a substantial proportion of a ceramic capable of thermionic emission in the space within the mold unoccupied by said core, compacting said mixture and said refractory metal layer so as to form a molded cathode into which said refractory metal layer is molded, removing said cathode from said mold, firing said cathode in an oxygen-free atmosphere at a temperature of from approximately 1,800 degrees C. to approximately 2,300

powdered mixture and said degrees. C. until said metal layer is firmly bonded to said cathode, and 'soldering a metallic cathode4 support to said bonded metal layer onsaid 4cathode by means `of a` solder havingA a high melting point..

12.` A method of joining :moldedthoria cathodes sef curelyto molybdenum supports comprising coating portions of a mold whichare spaced a predetermined distance apart with a thin coating ofpowdered molybdenum. sus

pendedin a suitable, binder, inserting4 adesired ,quantity of a powdered mixture containing a large percentage of thoria in said mold, 4retrieving said molybdenum from said portion of said moldand compactingpsaid thoria mixture and said molybdenum by exerting pressure onsai-d mold 0thereby forming a `molded thoria cathode at t both ends of which arlayer of said molybdenum is moldedl removing said cathode from said mold, ring saidy cathode ata temperature of atleast 1,800 degrees C. until saidN molybdenum layers are rmlybonded to said cathode; and sintering a molybdenum'cathode, structure to each of said `molybdenum layers on said cathode with molybdenum powder.

13. A method of manufacturing hollow cylindrical molded ceramic cathodes capable of being securely'joined to metal supports comprising coating ya portion of the said portion of said mold core and compacting said comminuted mixture and said refractory metal `by exerting.v pressure `on said moldto forml thereby acmolded cathode into the; inner periphery of l'which a layer of said refractory metal is molded.

14. A method of manufacturing molded ceramic cathodes capable of being securely joined. to metal supports comprising coating a portion of a mold Witha thin ,layer rif-powdered refractory'material suspended in a binder, inserting in said mold Va desired quantity of a powdered mixture containing a large percentage of a ceramic capable of therrnionic emission, removing said refractory metalfrorn said portion of said mold and compacting said vmixture and said refractory metal by exerting pressureon said mold thereby forming a molded cathode into whose surface a layer of said refractory metal'is molded, and firing said cathode until said refractory metallayer is rmly bonded to said ceramic cathode.`

`15;A method of manufacturing molded ceramic objects'capable of being securely joined to metal supports comprising coating a portion of a mold with a thin layer ofpowdered refractory material suspended in a binder, insertingmin said mold a desired quantity of comminutcd mixture containingy a largepercentage of a ceramic, removing said refractory metal from said mold and `compacting saidmixture and said refractorymetal by exerting pressure onsaidmold thereby forming a molded cathode into portions of whose surface a stratum of said refractory metalis molded,r removing said' object from said mold, and'liring said object-at a temperature of at least 1,800 degrees C. until saidI stratum of refractory metal is firmly bonded to said ceramic cathode.

References Cited in the le of this patent l UNITED" STATES PATENTS 974,3'89r` JonesJ Nov. l, 1910 1-,032g4slV smdith, July 9, 1912 1,-9814245 Pearcy; -c Nov. 20, 1934 2,350,5@4- Menihan` June 6, 1944 2,462,906. l Sauer-born Mar. 1, 1949; 

1. A METHOF OF MANUFACTURING MOLDED CERAMIC CATHODES CAPABLE OF BEING SECURELY JOINED TO METAL SUPPORTS COMPRISING COATING A PROTION OF THE INNER PERIPHERY OF A MOLD SLEEVE WITH A THIN LAYER OF POWDERED REFRACTORY METAL SUSPENDED IN A BINDER, INSETING IN SAID MOLD A DESIRED QUANTITY OF POWDERED MIXTURE CONTAINING A LARGE PERCENTAGE OF A CERAMIC CAPABLE OF THERMIONIC EMISSION, REMOVING SAID REFRACTORY METAL FROM SAID PORTION OF SAID MOLD SLEEVE AND COMPACTING SAID POWDERED MIXTURE AND SAID REFRACTORY METAL BY EXETING PRESSURE ON SAID MOLD. 